Her first battle with Stitch. That's right, a ten-year-old girl fighting a Destructive Alien that can grow four arms and can lift up 3000 times his own weight, and she holds her own, managing to throw him around the place while getting thrown down only twice. Not bad.
Stitch throwing out the Yokai who stole Kijimunaa's tree in Episode 3.
Yuna attempting to get Sparky for hurting Stitch in Episode 5.
Everyone pitching in to help Stitch take down Hämsterviel in the Season 1 Finale. There's also his battle with him, which ends with an epic line from Stitch.
Also, Tonbo's karate flip on Jumba and Officer Suzuki taking on Gantu.
Stitch: Get off of my island, you Ika Patooka! (Punches Hämsterviel in the face, and he ends up in jail.)
Season 2. Hämsterviel sends down a bug that messes with Stitch's Good Deed Counter. After finally having enough of the Counter glitching, Stitch throws it off and just decides to help out Kijimunaa when he is sick.
Also, from the first episode of Season 2, Jumba and Pleakly taking down Gantu with nothing but a water balloon and mosquitoes.
"I am Dracula Jr.!" That line just sells it.
Also, Frankenstein and the Werewolf appearing and taking down Penny and her gang, as well as Gantu.
Odie, the Fabric Yokai, saving Penny from cutting her dress by throwing thread at her and then hanging her in the air, donning her with a clown suit as well.
Yuna vs Audrey in "Stitch vs Captain Khan". Even though it was brief, they both matched each other's strengths.
Earlier, Kijimunaa taking on the fake pirates by batting pineapples at them.
Penny forcing Checkers off of her head in "Princess Penny".
Yuna and Penny's teamwork in "Link-Age".
From the same episode, Stitch using the Evil Experiments to help finish the construction of the school playground.
Jumba's giant tank that took down Hämsterviel, Gantu and Reuben in "Pteranodon!"
Ted saving Penny from the Christmas Tree monster he accidentally made in "We Wishy You A Washy Christmas".
Stitch using all the fishing rods to take down the monster too.
Stitch in Taro's scaring off Kenny in "Swapped."
The lengths Stitch went to in order to get Yuna's dad to come home for Dad's Day.
In the first episode, Jumba and Yuna save Stitch by crashing into Hämsterviel's ship to rescue Stitch.
Then, earlier on, Yuna calls Jessica out for calling Stitch a freak.
Yuna saving Hiroman from being crushed by a tree.
In Episode 2, after Jessica says that Yuna's Grandmother's Umbrella is stupid, Yuna proves her wrong by using it as a shield against Sample.
Hiroman: I like that umbrella, it works for you.
Episode 3 has Stitch searching all day for the handmade purse that Yuna gave to Jessica, but discarded.
In Episode 4, Hiroman, despite his appearance caused by Dorkifier, scores the goal by getting the opposing Goalie to let his guard down when laughing at him.
Yuna scaring her new school and later, Jessica, by telling tales that none of them would believe.
Stitch stopping PJ 2.0 from framing him by getting him to be part of a stage act.
Delores getting her School Team to win the TV Contest, and winning the affection of her opposing rival.
Also, Stitch defeating Spike 2.0 with sticks, in all four of his hands.
Stitch's rock throw at Gantu's Ship when he tries to escape.
Toriko and Makiko sacrificing themselves as reparation for eating the last chocolate bar. They tell Jessica to run, but this happens.
Jessica: I never leave a friend behind, and you're my friends!
In "Stitch's Birthday", Stitch, Yuna and Pleakly go to warn Jumba of Delia and Hämsterviel's backstabbing by using Nosy to blurt out the truth. Jumba then proceeds to call the two and call off their deal.
Before that' Yuna vs Jumba, especially their standoff.
Then, Stitch commands his soon-to-be cousins to repair the machine Past Jumba was going to use by experience to help get the energy needed from a planetary collision for making 626, therefore stopping Stitch from fading away in a way similar to Lilo And Stitch 2: Stitch Has A Glitch.
Delores freeing everyone from Hämsterviel's control through Wishy-Washy.
Every Experiment in the Season coming to help Stitch, evening out the odds.
Dark End: 25 vs 1? That's what I'm talking about!
Hiroman taking on Dark End with Soccer Balls, FLAMING Soccer Balls with Splodyhead's help.
Toriko and Makiko becoming animals once again and tackling Dark End.
After Stitch gets overpowered, everyone comes to his aid. Flashbacks of him with everyone starts to enter Stitch's mind, giving him enough of The Power of Friendship to take down Dark End and Jumba's message to get through to the Galactic Council to arrest Delia.